In recent years, various kinds of display devices for viewing a stereoscopic image (three-dimensional image) have been provided. One of such display devices adopts an autostereoscopic method (autostereoscopic 3D method). The autostereoscopic method, for example, simultaneously displays an image for the left eye and that for the right eye on a liquid crystal display (LCD) (a space division method), and controls directions in which a lenticular lens arranged on the LCD emits light beams corresponding to pixels within the images (a lenticular method). This enables the user to view the pixels of the image for the left eye with the left eye, and those of the image for the right eye with the right eye, thereby perceiving a three-dimensional image.
An autostereoscopic three-dimensional display which can display a three-dimensional image and a two-dimensional image on the same screen has recently been developed. In such an autostereoscopic three-dimensional display, a partial area within the screen can be used as a three-dimensional image display area (autostereoscopic 3D area) for displaying a three-dimensional image.
A personal computer including an autostereoscopic 3D display has also been developed. This computer can display a three-dimensional image on a partial area (autostereoscopic 3D area) within a screen while displaying a two-dimensional image on that screen.
It is, however, difficult to enable to simultaneously set a plurality of areas within the screen as autostereoscopic 3D areas because, for example, the cost increases. Therefore, exclusive control in which the number of simultaneously executable 3D-capable application programs is limited to one is conventionally used.
In the exclusive control, when a certain 3D-capable application program has already been executed, another 3D-capable application program does not start even if the user performs an operation for starting it.
Such conventional exclusive control in which an application program which the user tries to start is prohibited from starting, however, may give the user an unnatural impression. The user may misinterpret this to mean that the computer has failed. An error message may be displayed to notify the user of the reason the application program does not start. Displaying such a message, however, may complicate processing.